Fixes#6
### Motivation
As suggested here: https://pulsar.apache.org/docs/en/helm-deploy/#prepare-the-helm-release. The ```prepare_helm_release.sh``` script provided with this Helm chart can create a secret credentials resource and
> The username and password are used for logging into Grafana dashboard and Pulsar Manager.
However, I haven't been able to make use of such a feature for a number of reasons:
1. This secret doesn't seem to affect the ```pulsar-manager-deployment.yaml``` definition. Instead, the ```./templates/pulsar-manager-admin-secret.yaml``` seems to be the one providing the credentials for the pulsar manager (UI) (with the added possibility to overwrite via values.yaml at ```pulsar_manager.admin.user/password```).
2. Using the Pulsar chart as a dependency for an umbrella chart (this is currently my use case), will bring extra hassle that will make it very hard to have all resources follow the same naming structure, thus causing some resources to never be deployed successfully e.g.: ```./templates/grafana-deployment.yaml``` will complain that it couldn't find the secret created by the bash script. Attempting to fix this issue via the ```-k``` flag passed to the script will cause the JWT secret tokens to have a name that's unexpected by the broker, etc.
### Modifications
Decouple grafana credentials from pulsar manager via a new secret resource named ```./charts/pulsar/templates/grafana-admin-secret.yaml```.
Add credentials overriding via values.yaml in the same way as pulsar_manager (grafana.admin.user/password) & delete secret resource manipulation from bash scripts (cleaup_helm_release.sh & prepare_helm_release.sh)
### Verifying this change
- [x] Make sure that the change passes the CI checks.
### Motivation
As seen below, there is a fix for one of the Grafana dashboards that are currently broken in this project (available since version 0.0.5):
- [The Pulsar-topics metrics can't load in Grafana](https://github.com/streamnative/charts/issues/49)
Additionally, upgrading Prometheus to the latest version improves performance as seen here: https://prometheus.io/blog/2017/11/08/announcing-prometheus-2-0
### Modifications
Bring Docker images to their most up-to-date version (streamnative/apache-pulsar-grafana-dashboard-k8s:0.0.6, prom/prometheus:v2.17.2) to fix the following issues:
- https://github.com/streamnative/charts/issues/49 <- fixes Pulsar-topics metrics failure to load
- https://github.com/prometheus/prometheus/pull/2859 <- prevent escalation vulnerabilities by defaulting to the ```nobody``` user
**Note**: upgrading to the latest version of Prometheus (currently v2.17.2) caused the pod to fail with the following error: ```open /prometheus/queries.active: permission denied```. In order to fix this issue I followed the instructions from these 2 comments:
- [Permission denied UID/GID solution](https://github.com/prometheus/prometheus/issues/5976#issuecomment-532942295)
- [Unable to create mmap-ed active query log securityContext fix](https://github.com/aws/eks-charts/issues/21#issuecomment-607031756)
### Verifying this change
- [x] Make sure that the change passes the CI checks.
